1. Field of the Invention
This invention relates to a thermal head energy control apparatus, and more particularly to an apparatus for controlling energy applied to a thermal head when a stencil material is perforated on the basis of image data representing an image.
2. Description of the Related Art
In a stencil printer, a stencil is first made by perforating a stencil material on the basis of image data, for instance, obtained by reading out an original or transferred from a computer. Then printings are obtained by transferring ink to a printing medium such as printing papers through the perforations in the stencil.
When the stencil material is perforated on the basis of image data, that is, the stencil is made, the stencil material is perforated by applying energy (thermal head energy) to the stencil material through a thermal head according to, for instance, the kind of the stencil material.
However, since the stencil material is kept rolled until it is unrolled to transfer an image thereto, the stencil material is locally wrinkled according to the time from the time the stencil material is produced to the time it is used, the force applied thereto when it is rolled or the pressure which the stencil material roll experiences. Especially, it has been well known that the outer and inner parts of the stencil material roll are greatly different from each other in smoothness.
Accordingly, when the same thermal head energy is applied to the stencil material irrespective of its part, defective perforation can occur due to difference in smoothness, which can result in deterioration in printing quality.
In order to overcome such a problem, there has been made an attempt to smooth the wrinkle of the stencil material by applying heat and pressure to the stencil material by heat rollers provided between the stencil material roll and the thermal head.
However, this approach has not been effective since it is difficult to find the intensity of heat and pressure to be applied to the stencil material.